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GEOLOGY. — Lavas of Hawaii and their relations. Whitman Cross. 

 U. S. Geological Survey Professional Paper No. 88. Pp. 93, 4 

 plates. 1915. 



The Hawaiian Islands have been built up by a long continued series 

 of volcanic eruptions beginning at a point far west of the principal 

 islands of today. While basalt of a common type is the predominant 

 rock of the islands, there is much greater variety among the rocks 

 than has heretofore been recognized. As indicated by the work of 

 Cohen, E. S. Dana, Lyons, and Silvestri, the rocks range chiefly between 

 normal basalts rich in olivine, augite, and highly calcic plagioclase to 

 pyroxene andesites either free from or poor in olivine and containing 

 andesine or more richly sodic plagioclase. There are, however, more 

 basic rocks such as limburgite, nephelite and melilite basalt, and 

 picritic basalt, while xenoliths of peridotite are reported from several 

 islands. A soda trachyte is the most feldspathic rock so far collected. 



The chemical characters are discussed on the basis of 43 existing 

 analyses showing many rocks of the so-called alkaline type. These 

 analyses evidently do not cover the entire range of rock types but, 

 classifying the analyzed rocks in the "quantitative system," all but 

 the three most salic rocks come within the range of two classes, that is, 

 in Class III or the adjacent halves of Classes II and IV. 



The Hawaiian archipelago forms a simple petrographic province 

 whose rocks are clearly comagmatic and consanguineous. The region 

 is especially suited to furnish the means of testing several broad generali- 

 zations of the day regarding the genetic relations of igneous rocks. 



Each of the larger islands contains several kinds of rocks showing 

 important differences in both chemical and mineral composition and 

 conversely several kinds of rocks are known in all or nearly all the 

 larger islands. In view of the meagerness of our knowledge concerning 



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